[stem-ebola] PRO> Ebola virus disease - West Africa (194): bat immunity

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EBOLA VIRUS DISEASE - WEST AFRICA (194): BAT IMMUNITY CLUE
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Date: Thu 16 Oct 2014
Source: The Conversation [edited]
<http://theconversation.com/bats-immunity-may-hold-key-to-preventing-future-ebola-outbreaks-32633>


Bats are the natural host species for Ebola and a variety of viruses,
many of which can be fatal when transmitted to humans. More than 100
viruses have been identified in bats and this number is rising each
year.

African fruit bats first transmitted Ebola virus to [non-human]
primates and other species through contact with bat droppings,
half-eaten fruit, or bodily fluids of diseased bats. People are
thought to have contracted the virus through contact with infected
bats and [non-human] primates. Subsequent person-to-person
transmission occurs through direct contact with infected body fluids:
blood, saliva, mucus, vomit, urine, or faeces.

Interestingly, bats have the ability to harbour viruses such as Ebola
and don't display clinical signs of disease. Yet once the virus
infects other species, it has the potential to cause widespread death
and disease. How is it that bats are resistant to a disease that kills
up to 90 per cent of people it infects?

The impact of Ebola virus in people is largely the result of the
activation of the immune system, rather than the virus itself. During
the initial stages of infection, Ebola shuts off the immune response
to the virus, resulting in rapid viral replication and a delay in the
production of antibodies.

The immune system is initiated only once the virus is out of control
and then results in over-activation of the immune response. Although
the role of the immune system is to eliminate the virus, when it is
activated at extreme levels it becomes damaging to the host -- in this
case, an infected patient.

Like all haemorrhagic fevers, this results in widespread tissue
damage, leading to internal and external bleeding, decreased kidney
and liver function and ultimately, in many cases, death.

The Ebola outbreak in West Africa is the largest ever recorded and is
continuing to accelerate. Researchers and drug companies are racing to
develop treatments and vaccines targeting the Zaire ebolavirus, the
strain that is causing the current outbreak.

The 1st human trial to establish the safety of the vaccine and assess
the immune responses of volunteers is underway. The researchers hope
that by November [2014] there will be enough data to make an informed
decision about whether to deploy the vaccine in Western Africa.

So far, studies in monkeys have demonstrated that the vaccine provides
protective immunity for up to 10 months.

Unlocking the bat immune system
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Studying how bats control viral replication may unlock alternative
mechanisms for tackling Ebola as well as other new and emerging
infectious diseases. Increasing antimicrobial resistance of viruses,
bacteria and fungi, for instance, is becoming a global concern and we
need to think creatively to find solutions.

Bats and viruses have achieved an equilibrium that allows them to
co-exist. Clues from studies of bat genomes have revealed differences
in genes associated with the very early immune response that could
help bats respond to infections. These genes appear to be evolving at
a faster rate in bats compared with other species, providing evidence
that they are likely co-evolving with the viruses that bats carry.

Functional differences in the immune system may also play a role.
Unlike humans and mice, which activate their immune systems only in
response to an infection, bats appear to have certain components of
their immune system constantly switched on. This may allow bats to
control viral replication much more efficiently compared with other
species.

If we can redirect the immune responses of other species to behave in
a similar manner to that of bats, the high death rate associated with
diseases such as Ebola could be a thing of the past.

It's tempting to look to culling as the answer to deal with bats as
the natural hosts of Ebola. This suggestion was made during the
spillover of Hendra virus from bats to horses in Australia. But it is
not the answer; bats are an extremely successful group of mammals,
making up 20 per cent of all mammalian diversity. They are critical to
ecosystems, with roles in insect control and pollination.

Rather than persecuting bats, we need to unravel the secrets of the
success of this group of mammals. Understanding how bats control viral
replication would not only assist in developing future therapeutics
but may also help predict transmission events from bats into human and
animal populations.

[byline: Michelle Baker]

--
communicated by:
ProMED-mail from HealthMap Alerts
<promed@xxxxxxxxxxxxxx>

[Zoonotic viruses in over 15 virus families have been identified in at
least 200 bat species around the world. Bats infected with these
viruses seem to show no conspicuous signs of disease and they may be
persistently infected. It is clear that investigating the immune
system of bats is crucial to gain a better understanding of their role
as reservoirs of zoonotic pathogens. It has been suggested that bats
might be able to control viral replication through innate immunity.

Related to this, it has been hypothesized that innate immunity is
linked to flight activities. Flight increases body temperature, which
accelerates the rate of multiple immune responses in mammals,
including components of the innate and adaptive immune systems (see
<http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4012789/>).

Undoubtedly, a better knowledge of the immune system of bats will
enhance our capability to predict, prevent, control, and treat the
zoonoses transmitted by them. - Mod.PMB]

[See Also:
Ebola virus disease - West Africa (193): Senegal free, WHO, S. Leone,
Nigeria 20141018.2878044
Ebola virus disease - West Africa (192): WHO, S. Leone soldier, MSF,
new drug 20141016.2870865
Ebola virus disease - West Africa (191): Liberia, Sierra Leone,
volunteers, vaccine testing 20141012.2854716
Ebola virus disease - West Africa (186): WHO, Cuban HCWs arrive,
prevention 20141004.2832637
Ebola virus disease - West Africa (185): WHO, CDC, Liberia, vaccine
20141001.2823670
Ebola virus disease - West Africa (183): great apes as sentinels
20140930.2818170
Ebola virus disease - West Africa (182): vaccine, orphans, S.Leone,
prevention 20140930.2817719
Ebola virus disease - West Africa (180): S. Leone, Liberia, USA,
drugs, Guinea 20140928.2813292
Ebola virus disease - West Africa (179): Liberia, protection, aerosol,
prevention 20140927.2811394
Ebola virus disease - West Africa (177): WHO, quarantine, vaccine,
Liberia, surv. 20140926.2808526
Ebola virus disease - West Africa (175): CDC, Sierra Leone, drugs,
survivors RFI 20140924.2802601
Ebola virus disease - West Africa (168): MSF, volunteers, hiccups,
vaccine 20140917.2780781
Ebola virus disease - West Africa (162): WHO, volunteering, protection
20140912.2770539
Ebola virus disease - West Africa (161): hospital ships, military
medical aid 20140911.2767249
Ebola virus disease - West Africa (160): Senegal, Liberia, tests,
media 20140911.2766294]
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